As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries which exhibit high energy density and voltage, long lifespan and low self-discharge rate are commercially available and widely used.
As positive electrode active materials for such lithium secondary batteries, lithium-containing cobalt oxides such as LiCoO2 are mainly used. In addition, lithium-containing manganese oxides such as LiMn2O4 having a spinel crystal structure and the like, and lithium-containing nickel oxides such as LiNiO2, etc. are also used. As negative active materials, carbon-based materials are mainly used and use of lithium metal, sulfur compounds, etc. is also considered. In particular, since a theoretical specific capacity of pure silicon (Si) is 4200 mAh/g, which is dramatically higher than that of graphite carbon at 372 mAh/g, lithium secondary batteries using Si-based active materials attract great interest. In some cases, Si-based active materials mixed with carbon materials are used as an electrode.
However, when irreversible efficiency of negative electrodes is lower than positive electrodes, negative electrode active materials are added in excessively large amounts, negatively affecting battery energy density. In addition, in order to adjust irreversible capacities of negative electrodes, positive electrode active materials also should be added in excessively large amounts to correspond to the irreversible capacities of the negative electrodes.
Therefore, there is an urgent need for technology to resolve such problems.